In the past two or three decades diesel engines have increased power output per cylinder two to three times, but fuel injection systems which require very precise tuning and reliability have remained practically unchanged. The traditional design of the fuel system of such diesel engines includes a camshaft actuated from a crankshaft, individual plunger-type fuel pumps, fuel injectors, and different types of governors.
Lately designers and manufacturers of diesel engines, particularly marine diesel engines, have tried to introduce different types of electronic controls to existing conventional injection systems, such as camshaft driven unit injectors with electronic on-off controlled solenoid valves, or providing hydraulic actuators for conventional plunger-type fuel pumps. However, these recent improved fuel systems for diesel engines are more complicated, less controllable, more unreliable, and more uneconomical than heretofore.
Practically, when the operating condition of the fuel pumps in these fuel systems is changed due to cam, plunger or valve wear, the injection process becomes difficult to control regardless of the type of the associated electronic control. Each cylinder of the engine with this kind of injection system acts as an individual engine. With this arrangement it is difficult to balance power distribution between cylinders.
In multi-cylinder engines the power distribution between cylinders becomes uncontrollable which causes overloading of some cylinders and under loading of others. This results in failure of pistons, bearings, crankshaft, and other major engine parts and increased exhaust emissions. Variable injection timing (also known as VIT) devices using existing VIT controls to individual cylinders do not properly react to load and ambient conditions of various engine operations.
No engine or fuel injection equipment manufacturer heretofore, so far as is known, has attempted to directly control automatically the load sharing between individual cylinders, emission quality, and other major operating engine parameters. An electronically controlled functional algorithm or formula based on on-off principles cannot adequately react and govern existing conventional types of fuel injection systems. The very short time, only a few milliseconds, available for injection in diesel engines and the very high injection pressure, 1,000-2,000 bar, both present problems. They do not permit the utilization of a responsive and reliable system based on the principles of conventional injection systems elements. Fuel injection systems based on a crankshaft-camshaft drive and camshaft actuated fuel pumps are dynamically and hydraulically unresponsive, cannot be properly controlled, and react inadequately to changes which occur as a result of different load and ambient conditions during engine operation.
Other attempts to solve the problems associated with a fuel injection system operated from a crankshaft-camshaft drive have included a fuel injection system with two fuel injectors with different settings, or a complicated pre-injection pump arrangement. Both the pilot or pre-injection pump concept approaches have disadvantages. The high injection pressure (1,000-2,000 bars) acting on the plungers and associated valves causes them to deteriorate due to cavitation.
Conventional fuel injectors, by method of operation, are direct-acting relief valves. They operate on differential forces between fuel supply pressure and mechanical spring. In conventional fuel injection systems the load distribution between individual cylinders is uncontrollable. The failure of an individual fuel pump or fuel injector and related equipment on a multi-cylinder engine reduces the power of the engine by the amount which had been generated by the failed cylinder. The load which has been lost from the failed cylinder was consequentially distributed between the remaining normally operating cylinders. This causes uneven load distribution and overload to the entire engine when controlled by variable speed governors.
Variable speed governors, as analog devices, serve the purpose of maintaining a constant speed. So, in reaction to the failure of a single cylinder, variable speed governors increase fuel supply to the remaining operating cylinders causing overload and increasing torsional vibration and emissions of the engine. The disadvantage of these kinds of fuel systems has been proven over many years by different engine manufacturers. Fuel systems based on these principles are usually complicated, relatively unreliable and expensive.
Widely used in the engine industry are the conventional closed-type or Robert Bosch fuel injection elements. From a hydraulic definition they are direct-acting, unbalanced relief valves with different opening and closing characteristics. Injection pressure can be varied by these Bosch or closed-type fuel injection elements. Injection pressure of these valves depends only on the volume of the fuel pump and of the cross section of the injector atomizer holes.
Engine manufacturers have recently introduced another definition for the marine engine operation condition. The definition is called the mean continuous rating (MCR). Basically, this MCR definition allows marine diesel engines to operate at reduced power. For this reason, hundreds of fuel nozzles and fuel valves have been developed for the same engine. Practically, if the engine operator wants to change MCR of the engine new fuel injectors and fuel pumps need to be purchased. Only in this way can injection pressure be changed for existing fuel systems. However, changing MCR for an engine makes the previously purchased injection valves and related fuel injector equipment for that engine obsolete.